This invention relates to an improved locking arrangement for the oven latch mechanism in a domestic cooking appliance equipped with a self-cleaning oven. Such ovens have in addition to the normal cooking functions or modes, a self-clean mode in which the temperature is raised to a maximum temperature in the 750.degree.-950.degree. F. range to remove the food soil and grease spatter that accumulates on the wall of the oven liner by pyrolysis. In such high temperature ovens, it is of primary importance to latch the oven door before the cleaning cycle begins and to insure that the door cannot be opened during the period when the temperature is elevated to the self-clean temperature range.
In view of the convenience of automatic self-cleaning such ovens have become quite popular and a variety of arrangements have been proposed to perform the latching and locking functions.
One approach involves a relatively complex and costly mechanical locking structure equipped with a solenoid actuated locking mechanism controlled by a sequence timer. An example of such an arrangement is described in commonly assigned Re. 26,943 to Barber. The sequence timer is energized by selection of the self-clean cycle and latching of the door. An initial ten minute Wait period is provided during which the latch may be opened. The Wait period is followed by a 90 minute clean cycle, during which a solenoid controlled plunger prevents opening of the latch. The clean cycle is followed by a twenty minute Cool period. During this period the heating means is de-energized but the plunger continues to prevent opening the latch. At the conclusion of the Cool period the timer energizes the solenoid to move the plunger from its locking position permitting the opening of the latch. Another example of a solenoid actuated locking mechanism for a self-cleaning oven latch can be found in U.S. Pat. No. 3,831,580 to McClean.
Such an arrangement performs quite satisfactorily. However, it is mechanically and electrically relatively complex involving a solenoid and a number of relays and switches. In addition, since it is strictly timer controlled, it may result in the oven latch remaining locked longer than necessary particularly in those instances when the user elects to halt a self-cleaning operation prematurely.
A number of latching and locking arrangements using bimetal devices responsive to oven temperature in combination with the door latch mechanism are also known in the art. U.S. Pat. No. 3,416,515 to Mertler describes an automatic latching arrangement in which a snap action bimetal element responsive to the oven temperature automatically latches the oven door when the oven temperature exceeds the bimetal trip point. In this arrangement the bimetal is linked to the latch arm by a plunger. The snap-action movement of the bimetal to its latching position causes the plunger to move the latch arm into latching engagement with the door. The plunger also trips a switch operative to actuate an indicator lamp to indicate that the door is locked for self-cleaning. The disclosure also notes that the switch could also be used for some unspecified interlock or other control functions. No means is provided for the user to manually latch or unlatch the oven.
U.S. Pat. No. 3,438,666 to Erickson discloses a locking arrangement for a manually operable latching mechanism in which a blocking member is rotated into blocking relation with the door latch mechanism by the expansion of a bimetal coil to prevent opening of the latch when the oven temperature is above a predetermined value. In its latched position the latch actuates a switch which conditions the control circuit for operation only when the door is closed and latched. Additional examples of the use of a bimetal coil to rotate a blocking member into blocking relationship with the latch can be found in U.S. Pat. Nos. 3,540,767 to Siegel and 4,133,337 to Shea.
U.S. Pat. No. 3,638,638 discloses a latching and locking arrangement for a self-cleaning oven which employs a combination of two bimetal members in a pivoted lever configuration to move the free end of the lever assembly into locking position to prevent opening of the latch. The second bimetal, having negative deflection characteristics below a certain temperature, cooperates with the main bimetal to aid in movement of the locking means into locking position as the oven temperature rises and out of locking position as the temperature falls at the beginning and end of a self-clean cycle respectively. The bimetals are arranged to reduce the temperature differential at which locking and unlocking would occur using a single pivoted lever bimetal arrangement.
The foregoing latching arrangements involving coiled bimetal devices or multiple bimetal elements involve relatively complex bimetal structures which respond gradually to temperature changes. In addition, no provision is made for preventing operation in the self-clean temperature range in the event the bimetal fails to move to the locking position.
It is therefore an object of the present invention to provide a relatively simple inexpensive locking arrangement for a self-cleaning latch mechanism which is manually operable by the user and which provides snap action movement between the locking and unlocking position for positive locking action at the predetermined trip temperature.
It is a further object of the present invention to provide a locking arrangement of the aforementioned type which includes fail safe means for positively detecting locking movement of the locking means and prevents operation of the oven in the self-clean temperature range if the locking member fails to move to its locking position.